The present invention relates to a route that links networks, and more particularly to a route that transfers packets using a virtual interface (that links plural networks using a virtual channel on one ATM (Asynchronous Transfer Mode) physical interface). The present invention also relates to a routing method suitable for a route.
Conventionally, that type of routing method embodied in the route is used to reduce a table retrieving operation needed in the main routing process and to improve the table retrieval efficiency and the packet relaying capability. Such a routing method is disclosed in the JP-A-152655/1994. According to the prior art routing method, a local area network connected by a physical interface has an address table which can store a set of a destination address and a transmission address of a network layer as well as relay history information during a packet transfer operation (the header of a data link layer and a transmission destination interface). The speed of the relay process can be improved by storing various pieces of information into the address table at the time a first packet is transferred and then transferring following packets by using the address table, so that the main routing process can be omitted.
However, one problem of with the prior art routing method is that when the address of a next hop in the network layer is a virtual interface such as Logical IP Subnet in an IP over ATM, packets cannot be transferred at high speed because a table retrieval must be performed for a call sent from a destination at a packet transmission time. The reason is that packets cannot be transmitted if, in the routing process by a virtual interface, an interface to which a packet is transmitted is not determined and a call connected with the next hop over a packet relay route is not retrieved. In other words, packets cannot be transferred at high speed because the virtual interface must first be set up, and then the call must be retrieved for transfer. The second problem is that, in a connection oriented-type communication lip IP over ATM, a connection is established by originating a call on a packet trunk line to the next hop when packet relaying (i.e., through the ATM network) is necessary, but the call is disconnected when packet relaying is unnecessary. In that case, the address table can not deal with the change in the call state at the ATM side to delete the entry for the disconnected call because the retrieval key for the table is the transmission source address and the destination address in the network layer.
The present invention is made to solve the above-mentioned problems. The objective of the present invention is to provide a route that executes a high-rate packet transfer process with an address table while a virtual interface is being used, so that the conventional routing process can be omitted.
Another objective of the present invention is to provide a routing method that executes a high-rate packet transfer process with an address table while a virtual interface is being used.
The objective of the present invention is achieved by a route that operates in an ATM-LAN environment which implements RCF1577 xe2x80x9cClassical IP and ARP over ATMxe2x80x9d (hereinafter referred to as IP over ATM) and has virtual interfaces, the route having an address table in which a record is created for a message at the time the first packet in the message is transmitted. The record is comprised of a destination address in the network layer, an address of a next hop on a packet relay route (or simply a network layer destination address when a packet can be directly transmitted to its destination without a next hop), and additional packet transmission information.
The additional packet transmission information comprises the of a packet a destination address of a network layer and an address of a next hop at a packet transfer time, a header of a data link layer and a transmission destination interface when a packet is to be transmitted to a LAN interface, and call information on an ATM side when the packet is to be transmitted to an ATM interface. As a result, subsequent packets in a message are directly transmitted to a physical interface using information in the record created in the address table when the first packet in the message was transmitted, without executing a routing process.
In the route, the address table also stores an aging timer for aging a table entry. The address table is retrieved by using as a search key a destination address of a network layer. An address table entry is removed by using as a search key the address of a next hope of a network layer. The address table stores a record including the address of a next hop and packet transfer information by using as a search key a destination address of a network layer.
Moreover, according to the present invention, a routing method suitable for a route that operates in an ATM-LAN environment which implements and has virtual interfaces, comprises the steps of preparing an address table in which entries, each comprised of a destination address of a network layer, address of a next hop on a packet relay route (a destination address of a network layer when a packet can be directly transmitted), and packet transmission information are stored, retrieved, and removed as single units. The packet transmission information of each entry includes a destination address of a network layer and a address of a next hop at a packet transfer time, a header of a data link layer and a transmitted interface when a packet is transmitted to a LAN interface, and call information at an ATM when a packet is transmitted to an ATM interface, and directly transmitted a packet to a physical interface using the address table storing the packet transmitted from each interface, without executing a routing process.
The routing method further comprises the step of omitting a routing process when packet transfer information is obtained by retrieving the address table and performing a conventional routing process when packet transfer information is not obtained by retrieving the address table.
In the routing method, the routing process omitting step comprises the steps of executing LLC (Logical Link Control) Encapsulation when an interface to which a packet is transmitted is an ATM interface, as a result of packet transmitting information, and directly transmitting packets to the ATM interface based on VPI/VCI of packet transfer information.
The routing method further comprises the step of performing an address entering process, in addition to a conventional routing process, when packet transfer information is not obtained by retrieving the address table.
The routing method further comprises the steps of retrieving an ATMARP table of a virtual interface obtained by the routing table retrieval when an interface to which a packet is transmitted is an ATM interface, issuing a connection open request according to the content of an entry of the ATMARP table when the ATMARP table exists, and issuing a connection open request after the ATMARP process when no ATMARP table exists.
According to the present invention, where a virtual interface is used, packets can be effectively transferred at a high speed by entering call information into an address table and using it for the routing of packets.